Assimilation of selenium from phytoplankton by three benthic invertebrates: effect of phytoplankton species

Phytoplankton are an important source of selenium (Se) for aquatic invertebrates, which accumulate Se primarily through dietary ingestion. The extent to which Se bioavailability varies among different phytoplankton species could help explain different bioaccumulation patterns observed for invertebrates in nature. We measured the efficiency with which 3 benthic invertebrates assimilated Se-75 from 5 phytoplankton species using standard pulse-chase techniques. The invertebrates included the amphipod Leptocheirus plumulosus and the bivalves Macoma balthica and Potamocorbula amurensis. The phytoplankton species included Cryptomonas sp. (Cryptophyceae), Gymnodinium sanguinem (Dinophyceae), Phaeodactylum tricornutum (Bacillariophyceae), Synechococcus sp. (Cyanophyceae) and Thalassiosira pseudonana (Bacillariophyceae). The range of Se assimilation efficiency (AE) by L. plumulosus (32.1 +/- 1.8 to 69.5 +/- 7.1%) was the lowest of the 3 organisms. No relationship was observed between the proportion of Se in algal cell cytoplasm and Se AE by L. plumulosus, which is consistent with findings for assimilation of other trace elements by this organism. Se AE by M. balthica (range: 58.0 +/- 3.2 to 92.3 +/- 6.0%) varied according to the proportion of cytoplasmic Se in algal cells (p < 0.0001, r(2) = 0.868). P. amurensis assimilated between 78.3 +/- 2.0 and 88.9 +/- 3.6% of Se from algal cells, and the relationship between cytoplasmic Se and Se AE was described by the following equation: Se AE = 69.2 +/- 0.22 x (% cytoplasmic Se) (p = 0.003, r(2) = 0.405). This relationship suggests that P. amurensis assimilated non-cytoplasmic Se from phytoplankton, perhaps through utilization of the glandular digestive pathway. Consistently high Se assimilation from algae by P. amurensis may contribute to elevated Se concentrations observed for this organism.